Method for conditioning wellbore fluids and sucker rod therefore

ABSTRACT

Invention refers to a method for conditioning wellbore fluids and to a sucker rod to accomplish the method used in the field of petroleum production. The method the invention refers to involves fact that the injection of the conditioning fluids is done directly through the sucker rods, from the surface, concomitantly pumping (producing) the well, being possible that the conditioning fluid be distributed either in the producing tubing or in the wellbore, or even in the reservoir rock around the wellbore, concomitantly pumping the well. The sucker rod designed for the application of the method is made of steel and it has two sucker rod heads ( 1 ) which are tubular, welded to the ends of a tube ( 2 ) made of steel, thus forming a continuous tube through which a fluid can flow or an electric or optical cable can be pulled through, or set inside.

Invention refers to a method to condition wellbore fluids and sucker rodto accomplish the method, used in the field of petroleum production.

Downhole pumping of wellbore fluids is the most frequent method used forsecondary recovery of crude oil in petroleum production. Downholepumping involves procedures and devices through which the pumping energygets to the wellbore fluids, so that wellbore fluids move up thedownhole, to the surface, through production tubing. Devices used forthis purpose are amongst the most diverse in the industry, though onlyfew models made inroads thus getting standardized. They are genericallyknown as downhole plunger pumps, PCP (Progressive Cavity Pumps), ESP(Electrical Submersible Pumps), and “screw” pumps.

From a constructive stand point, the devices used for downhole pumping,no matter the pumping option per se, have the following components: apart, the driver, where mechanical energy is generated, another parttransmitting mechanical energy previously generated to the pump and thepump itself. Pump transfers the mechanical energy brought from surfaceto the wellbore fluids, turning it into pressure. In the oil field, theelectrical motor imposed itself as the device of choice in generatingmechanical energy to drive the pump, though there are many applicationswhere one may see steam driving, hydraulic or pneumatic driving asalternate options to drive the pump. Mechanical energy from the drivercan be delivered to the pump either through sucker rods (in this casethe driver being at the surface and the pump downhole), or can beproduced and used locally. This second option is so-called “bottom holedriver” or “direct drive”; e.g. PCP pumps driven through bottom holedrivers, “screw” pumps driven through bottom hole drivers or ESP pumpsdriven in the same way.

Producing petroleum wells involves a wellbore to connect reservoir tosurface. Wellbore breaks into the physical and chemical equilibriumbetween reservoir fluids and reservoir rock. Breaking physicalequilibrium leads to an imbalance of pressures which in turn leads to anet flow, reservoir rock fluids flowing out into wellbore, until a newphysical equilibrium reached (one should note too a temperatureimbalance, but this is not relevant for scope of our discussion). At theon-start, the pressure imbalance between surface and reservoir rock islarge enough and reservoir fluids reach surface at own expense. Overtime, pressure imbalance decreases and at a certain juncture in time oneneeds to add energy to the reservoir fluid, to bring it to surface.That's the on-start of well pumping, various devices being in use forthis service.

Breaking the chemical equilibrium brings a different set of imbalances,more difficult to lump into a simple pattern, though same equilibriumprinciple applies. Most common alteration encountered is a phase change.New phase occurs while producing reservoir fluids—e.g. dissolved gas mayevolve from liquid; solubility of some components in the reservoir fluidmixture changes so drastically that a solid phase occurs—scale forms,both of organic and inorganic origin. Reservoir fluids also interactchemically with wellbore itself and wellbore equipment, corrosion beingthe most common phenomena encountered.

Another, more subtle consequence, is a change in the interaction degreebetween reservoir rock (matrix) and reservoir fluids trapped in.Reservoir matrix attrition occurs as soon as reservoir fluids startflowing and reservoir fluids mechanically entrap loose fragments off thereservoir matrix, in their flow to surface. Together they lead to aprocess known as reservoir matrix damage, which impact badly producingthe well.

Science and technology tried to find ways and improve means to copebetter with intricate consequences of producing a well, and particularlypetroleum wells.

One such task is to pump wellbore fluids to surface concomitantlycontrolling their behavior and aggressivity, such that to counteractpotential damages. Thus, the wellbore fluids, the wellbore itself oreven the reservoir rock nearby, needs conditioning. More specifically,conditioning is done to control scaling of wellbore, pump, tubingstring, and casing, to limit wellbore fluids corrosion or to improvetheir flowing properties. Conditioning nearby wellbore reservoir rocktries to maintain or improve reservoir matrix flow characteristics(filterability). In order to condition wellbore fluids, wellbore orwellbore reservoir rock nearby one has to add conditioning agents(dilutants, solvents, steam, hot water, specialty chemicals) toproduction tubing, casing or wellbore, or injected them into thereservoir rock, either continuously or in batches, either during pumpingthe well or when pump shuts down. Conditioning wellbore fluids andconcomitantly pumping the well is not an easy task because conditioningprocess and its tools interfere with the pumping process, the pumpingdevice and/or the pumping arrangement.

Attempts have been made to find answers to this challenge above. Assuch, patent U.S. Pat. No. 5,924,490 discloses a solution for a tool tocondition wellbore fluids upstream the pump (patent refers to a plungerpump), in the annulus formed between production tubing and sucking rods,as well as for conditioning wellbore and wellbore fluids for naturallyerupting wells only (note: no pumping is required for naturally eruptingwells). Authors achieve the task to condition the wellbore fluidsflowing in the annulus between the production tubing and sucking rods byreplacing some of the standard sucker rods with hollow sucker rods andinjecting the conditioning agent through such hollow sucker rods train,down to a disbursement valve installed at the end of the hollow suckerrods train, upstream the plunger pump. This way the author only allowsthe conditioning agent to interact with the wellbore fluids insideproduction tubing. No conditioning of the wellbore or of the reservoirrock itself is possible under such arrangement because tubing andplunger pump assembly form a closed container which only allows well'sinflow to be transferred to surface.

Another patent, WO-A-011187, describes an invention where an alternateplunger pump arrangement is proposed, in order to cope better withpresence of sand in the wellbore fluids, as sand extremely damaging tothe sucker rods. To avoid sandy wellbore fluids interact with the suckerrods while pumping, the authors make use of a second string ofproduction tubing, first production tubing string being used as aninjection string and protector for sucker rods. A side embodiment of theinvention describes an approach wherein the author proposes to use thenew dual string production system in a different arrangement where onemay replace plunger pump with a progressive cavity pumping system, andwhere, through adequate piping configuration, the production tubingconnects to the progressive cavity pump hollow rotor and to the secondproduction string. By its design, conditioning wellbore fluidsdownstream the pump it is possible but not the reservoir rock. The useof the second production tubing to prevent wellbore fluids frominteracting with the sucker rods doubles the production string, turningit extremely expensive. It leaves application facing great challengessince substantial alteration of exiting field infrastructure requested.

Conditioning wellbore fluids, wellbore or reservoir rock nearby meansproduction disruption in many instances: shut the well in, pull suckerrods string out, condition the wellbore or the formation, set suckerrods string and pump back into the well and resume production.Associated to production disruption is production loss. All these meansupplementary investment and costly logistics, thus leading to increasedcost of producing the well. The above-mentioned disadvantages have as astarting point existing configuration of sucker rods and pump assemblyused to pump the well.

For historical reasons, as well as because of infrastructure on site,delivering mechanical energy to PCPs or to screw pumps is done(nowadays) through the same sucker rods strings used for downholeplunger pumps. There is one major difference, though, and that has to beconsidered while comparing driving PCPs and “screw” pumps to plungerpumps. While transmitting mechnical energy to the pump, the sucker rodsused to drive downhole plunger pumps move up and down, axially; thesucker rods used to drive PCPs or “screw” pumps rotate.

The sucker rods used in the oil field are nowadays standardized, allsucker rods manufacturers following API 11B standard (American PetroleumInstitute).

Such sucker rod is a continuous full bodied metallic bar, with both endsprofiled and threaded to allow end-to-end connection in a sucker rodsstring. String thus made is used to transmit mechanical energy from thedriver (at surface) to the pump (downhole).

Using full bodied sucker rods strings leads to extra cost, involvessupplementary, costly logistics, and special operations and lostproduction is associated with, whenever the wellbore fluids, thewellbore itself or the formation pay zone has to be conditioned, asoutlined above.

Another disadvantage of using classical sucker rods pumping technologyis that it renders as expensive and non-attractive live data gatheringfor parameters like the bottom hole temperature and pressure, flowingproperties of the wellbore fluids, or the pumping regime. Bringing theinformation from bottom hole transducers to the surface, while pumpingthe well, it involves the use of special data cables inserted in theannulus between the production tubing and the production casing, anddesigned to stand the aggressivity of wellbore fluids, as well as thecombined effect of temperature and pressure. For special purposeapplications alternatives exist but they involve converting the electricsignals from bottom hole transducers in sonic or electromagnetic wavesbeamed to the surface, option even more expensive and difficult toimplement.

One may encounter similar troubles when direct drive applications areconsidered for PCPs, screw pumps or ESPs where the use of bottom holeelectric motors is needed. Bringing the power to the bottom holeelectric motors requires power cables usually inserted in the holethrough annulus and designed to stand the aggressivity of wellborefluids, as well as the combined effect of temperature and pressure.These cables are very expensive and sometimes this renders bottom holedirect drive technique as non-attractive.

An alternative option to driving downhole pumps (no matter whetherplunger, PCP, screw or ESP) has been designed and it involves the use offlexible coiled tubing instead of classical sucker rods. This option ismore expensive than traditional sucker rods driving and consequently oflimited use. To compound the issue, using coiled tubing means thatspecial infrastructure must be available on site. Because of that thecost of replacing the classical sucker rods technology becomesprohibitive.

The technical problem this invention intends to solve addresses devisinga method to condition wellbore fluids, or the wellbore itself or thereservoir rock, concomitantly pumping the well, with a special emphasison using the existing infrastructure in place in the oil field. To theseends devising a sucker rod designed to help achieving this task isneeded.

Conditioning the wellbore fluids, the wellbore itself or the reservoirrock and concomitantly pumping the well, as devised through thisinvention, involves injecting the conditioning fluid from surface intothe wellbore, directly through the sucker rods. Thus solving thetechnical problems described above. Injecting pressure of conditioningfluid will be adjusted from the surface, in accordance with the scope ofinjection, whether placing conditioning fluid in the tubing, or wellboreor injecting it into the reservoir rock. Through adequate devices,conditioning fluid can be distributed either in the production tubing,wellbore or injected into the reservoir rock, as needed.

The sucker rod as devised through the present invention consists of asingle continuous flowing tube made of two sucker rod heads attached bywelding to both ends of a steel tube. The conditioning fluid can flowthrough this continuous tube, thus achieving the scope of conditioningthe wellbore fluids or the wellbore and concomitantly pumping the well.The sucker rod head has a hole drilled into. This hole is cylindricalthrough the whole section between the beginning of the thread of thesucker rod head, through the wrench square and the lower third height ofthe sucker rod bead. The hole continues conical through the rest of thesucker rod bead height and ends cylindrical in the welding section ofthe sucker rod head. A radius connects the conical section of the holeto the last cylindrical section, designed to function as a stress reliefsection.

The conditioning method presented in this invention and the hollowsucker rods devised for it can be applied directly in oil filed pumpingapplications using the infrastructure and logistics available on site tohandle traditional sucker rods. Simultaneously, using hollow sucker rodscreates a premise to condition wellbore fluids while pumping the well(through injecting the conditioning fluid through the hollow suckerrods) still using the infrastructure and logistics available on site tohandle traditional sucker rods. In the case of PC pumping technology,using hollow sucker rods creates a premise to condition the wellbore oreven the reservoir rock without pulling the sucker rods string out thewell. Thus, the immediate advantage of using hollow sucker rods forwells already equipped with PCP. Plunger pumping as well as screwpumping technologies will also benefit using hollow sucker rods andconditioning method presented in this patent application.

Live data gathering as well as PCPs, screw pumps or ESPs direct driveapplications will benefit from using hollow sucker rods. Informationfrom bottom hole transducers can now be transmitted to surface viaadequate electric or optical data cables inserted through the hollowsucker rod string, while pumping the well. When direct driveapplications are considered, one has to bear in mind that electricmotors have to be attached directly to the pump, downhole. If hollowsucker rods technology considered, the power can be brought anddelivered to the bottom hole electric motor via power cables insertedinto the hollow sucker rod string. Data and power cables protection canthus become lighter since no need for cables to stand the aggressivityof the wellbore fluids or combined effect of temperature or pressure,thus the cost of these special cables dropping. Bottom hole live datagathering or direct drive becomes more attractive and easier toimplement.

Examples depicting the conditioning method presented in this applicationand the hollow sucker rods devised for it are presented following afterin FIGS. 1-3:

FIG. 1, shows a front view of a hollow sucker rod;

FIG. 2, shows a front view & partial resection of hollow sucker rod fromFIG. 1;

FIG. 3, shows a schematic view of a typical PCP pumping arrangementusing a hollow sucker rods string.

The conditioning method as devised through the present applicationinvolves the preparation of conditioning fluid, dozing and pumping itinto the wellbore while producing the: well, interacting theconditioning fluid with wellbore fluids, the wellbore itself or thereservoir rock and changing accordingly the properties of wellborefluids or reservoir rock around the wellbore. Specific to the method isthe pumping phase of the conditioning fluid. The conditioning fluidflows directly into the wellbore, through the hollow sucker rods,concomitantly with pumping wellbore fluids to surface. Transmitting thepower needed for pumping from surface to the point of use (the downholepump) concomitantly with conditioning the wellbore fluids becomes thuspossible through this new approach. Conditioning fluid that is pumpedinto the wellbore through the hollow sucker rods can be directed intothe production tubing or the wellbore while pumping the well, or can beinjected into the reservoir rock around the wellbore without pulling outthe hollow sucker rods string. Adjusting the injection pressure andusing adequate fluid diverting devices controls the place where theconditioning fluid is disbursed into the wellbore. All conditioning andpumping phases are done traditionally.

The shape and size of hollow sucker rod as devised through the presentinvention follow API 11B standard. The hollow sucker rod consists of twotubular pieces 1 named sucker-rod head attached to a steel tube 2. Wallthickness of the steel tube is sized adequately to serve the process.Attaching sucker-rod heads to steel tube is by welding, thus obtainingthe final product, a continuous tube through which fluid can flow—thehollow sucker rod. Assembling hollow sucker rods together results into ahollow sucker rod string that can transmit power from the surface to thepoint of use (the downhole pump) concomitantly allowing fluid to flowthrough it. Length of hollow sucker rods is between 8.32 meters and 9.99meters, shorter versions (“hollow pony rods”) being possible to be madethrough same process (the equivalent of pony rods from API 11B).

The sucker-rod head 1 consists of a threaded pin section a (thread asper API 11B), that continues with a section b that serves as a stressrelive section, after which section c continues, called shoulder,followed by a “wrench square” d. Wrench square d allows the applicationof torque, via a wrench, when assembling/dis-assembling hollow suckerrods into a string. Wrench square d continues with a thicker section e,called “bead”, and a welding section f, cylindrical. Inner hollow g ofthe sucker-rod head 1 is cylindrical through out section g′, from topend of threaded pin all along last third of the “bead” e, continuesconical through out section g″ and terminates with another cylindricalsection g′″ through out the welding section f. Between section g″ andg′″ a radius r is allowed, to act as a stress relieve section. The steelthe hollow sucker rod is made of is selected such that all prerequisitesin terms of torque, elongation and combined torque and elongation shouldbe fulfilled, including fatigue and corrosion resistance.

Hollow sucker rods can be assembled into a hollow sucker rods string andthis is presented in FIG. 3 for a typical PCP application. One can seethat the pumping unit consists of a drive unit A, made of an electricalmotor 3 delivering power to a gear box, a coupling 4 and a drive head 5.Stuffing box B on the hollow polished rod 6 insures that injection fluidcan be pumped through the hollow sucker rod string without leaking.Stuffing box C seals the hollow polished rod 6 against the productiontubing, such that no wellbore fluids spill into the environment. Hollowpolished rod 6 connects to the hollow sucker rod string D via a shorterhollow sucker rod, similar to a pony rod but hollow. Hollow sucker rodstring D inserts into the production tubing 7 and is made of hollowsucker rods 8 connected together via standard threaded connectors.Hollow sucker rod string can be terminated with an injection valve 9,through which conditioning fluid can be disbursed in the annulus betweenthe production tubing and the sucker rod string, above the PCP pump.Power is transmitted from surface to the PCP pump E via the hollowsucker rod string D. PCP pump E can be either traditional or hollowrotor PCP. Anchor F and stabilizer 11 anchors and centers the PCPdownhole. In this later case conditioning fluid can be disbursed eitherin the production tubing or downhole into the wellbore while pumping thewell. Reservoir rock around the wellbore can also be conditioned if whenconditioning fluid injected via hollow sucker rod string.

If live data gathering is to be considered, data cables transmittinginformation from downhole transducers to surface run through the hollowsucker rod string. Data cables, either electric or optical, are thusprotected against the aggressivity of the wellbore fluids and the impactof pressure. Similarly, when direct drive applications considered thepower cable runs through the hollow sucker rod string, connectingelectric motor downhole to surface power.

When a plunger pump considered the PCP pump E has to be replaced with adownhole plunger pump, and the drive unit with a pump jack, the rest ofthe configuration staying same. In the case of a “screw” pump the PCPpump E is replaced by the screw pump itself, not other changes beingnecessary to configuration presented in FIG. 3. In both cases (downholeplunger pump and “screw” pump) one can condition the wellbore fluidswhile pumping, injecting conditioning fluid through the hollow suckerrod string D into annulus between production tubing and hollow suckerrod string, through injection valve 9, above the pump. Because of theway these pumps are designed, conditioning the wellbore or the reservoirrock around the wellbore through injecting conditioning fluid throughhollow sucker rod string is no longer possible.

1. Method for conditioning wellbore fluids and/or wellbore itself orreservoir rock around the wellbore, including preparation ofconditioning fluid, dosing and pumping conditioning fluid under pressureinto the wellbore, interacting the conditioning fluid with the wellborefluids, the wellbore itself or the reservoir rock around the wellbore,followed by consequent and adequate change of their propertiescharacterized by the fact that, through a continuous tube connectingsurface to the wellbore, tube consisting of a train of hollow suckerrods assembled together with a hollow PCP rotor, conditioning fluid canbe pumped directly from the surface into the wellbore concomitantly withpumping (producing) the well, thus being possible to distribute theconditioning fluid either in the wellbore or even in the reservoir rockaround the wellbore, concomitantly with pumping (producing) the well. 2.Method as per claim 1, characterized by the fact that through adjustingconditioning fluid injection pressure, one can adjust the place wherethe conditioning fluid is placed in the wellbore interacted with thewellbore-fluids, the wellbore itself or reservoir rock around thewellbore.
 3. Sucker rod, made of steel, profiled and threaded at bothends, characterized by the fact that it has two sucker rod heads (1)which are tubular, welded to the ends of a tube (2) made of steel, thusforming a continuous tube through wich a fluid can flow or an electricor optical cable can be pulled through, or set inside.
 4. Sucker rod asper claim 3, characterized by th fact that the head of the sucker rod(1) has an inner hole (g), cylindrical in the section (g′) from the topend of the sucker rod (1) thread (a) down to approx. the lower end ofthe upset bead (e) of the head of the sucker rod (1), the cylindricalsection (g′) being followed by a conical section (g″) and ending with asection (g′″), cylindrical all the way through the welding zone (f) ofthe head of the sucker rod, between zone (g″) and (g′″) existing aradius (r) which works as a stress relief.
 5. Sucker rod as per claim 3and 4, characterized by the fact that it can be assembled into a hollowpumping string which, when applied together with a hollow rotor of a PCPpump, it can be used to pump the well concomitantly with injectingconditioning fluids or, if necessary to protect electrical/opticalcables passing through, cables transmitting to the surface signals aboutproperties of the wellbore fluids or pump status, signals generated byadecquate transducers munoted on the sucker rod string or pump itself,or transmitting power from surface downhole, to the downhole electricalmotors used to drive PCP, “screw” or ESP pumps.
 6. Hollow PCP pumpingstring made of steel characterized by the fact that it consists of a PCProtor which is hollow, made of steel, assembled together with a train ofhollow sucker rods, each sucker rod being made of steel, profiled andthreaded at both ends and, having two sucker rod heads (1) which aretubular, welded to the ends of a tube (2) made of steel, thus forming acontinuous tube connecting surface to the wellbore, through which afluid can flow or an electric or optical cable can be pulled through orset inside.
 7. Hollow PCP pumping string as per claim 6, characterizedby the fact that, concomitantly with pumping the well, it can be used toinject conditioning agents or, if necessary, to protectelectrical/optical cables passing through, electrical cables thattransmit to the surface the electrical signals about properties of thewellbore fluids or pump status, generated by adequate transducersmounted on the sucker rod string or pump itself, or that transmit powerfrom the surface downhole to the downhole electrical motors used todrive PCT, “screw” or ESP pumps.